Glass composition and method of making it



r' 2,964,414 fi P 'tented Dec. 13, 1960 GLASS COMPOSITION AND METHOD or MAKING rr RobertiH. Dalton and George B. Hares, Corning, N.Y., assignors to Corning Glass Works, Corning, N.Y., a corporation of New York No Drawing. Filed Apr. 23, 1958, Ser. No. 730,253

4.Claims. (Cl. 106-53) BaO, have substantially higher resistivities when sufficient Rb O is present in the glass sothat the ratio of Rb O to the total alkali metal oxide content is at least 1/20. Compositions containing a smaller-proportion'of the allcali metal oxide as Rb O do not exhibita substan' tial increase inresistivities. While there does not appear to be an; upper limit to theproportion of al'kali metal .oxide which can be added as Rb O, for practical reasons we prefer not to exceed the proportion .of'3 parts Rb O to 10 parts total alkali'metal oxide. 7 V

Glasses containing'by weight less than 15 SiO less than 5% PhD, .or more than 60% .PbQare generally .not used for the purposes of this invention. There is no definite upper limit for the alkali metal oxides, but on account of the approach of instability and for other practical reasons we prefer to use not more than a total of about 25% V of the latter.

electronic discharge tubes, and the like. These glasses have particular utility because they can .be sealed to fabricated glass parts at temperatures which will not have high enough volume resistivities to act as insulating the glass and decrease its tendency to devitrify. distort the shape of these previously fabricated parts and" T1" in ohms per unit length of a uniform bar of unit sectional 4 area.) Hence,.they are particularly useful for themanu:

The soft glass compositions which have heretofore been 7 used for such applications have included silica, lead oxide, and one or more of the usual alkali metal oxides. While the term alkali metal oxides is accepted in the glass-making art as meaning soda and potash and in some instances lithia (Glass Glossary, The American Ceramic Society Bulletin, vol. 27, No. 9, pp. 353-62, 1948), it is hereinafter used in the specification and claims in the literal chemical sense to mean an oxide of any of the elements of the first group of the periodic table, consisting of lithium, sodium, potassium, rubidium, and cesium. Anobject of this invention is to increase the resistivity of soft electrical glasses.

Other objects will become apparent to one skilled in the art from the following description taken together with the illustrative examples which are given byway of ex-' planation and should not be deemed to be limitations on the scope thereof.

. All percentages and proportions of constituents of glass compositions hereinafter set forth are by weight unless otherwise stated. 7

We have found that the resistitivities of soft electrical glass compositions can be substantially increased by including Rb O in the glass in a proportion of at least 1 part Rb O to 20 parts total alkali metal oxide. Moreover, these increased resistivities can be obtained without appreciably altering other advantageous properties of the glasses, 'ifso desired, since it is possible to maintain the total moles of alkali metal oxides in a given weight of these glasses the same as in the prior glasses.

,More'specifically, we have found that soft electrical glasses containing about 5% to 60% PhD, about 5% to 25% alkali metal oxides, and more than 15% S10 and optionally containing up to a total of 20% of other compatible inorganic oxides such as A1 0 MgO, CaO, and

Other compatible oxides may be added in total amounts by weight not exceeding 20% to modify other desirable qualities to the glass. Thus alumina may be added in an amount up to 5% to increase the chemical durability of Glass modifiers of the second group in the periodic table such as CaO, BaO, and MgO, may be added individually or in combination in amounts not exceeding 15%, to eifect small changes in working properties such as melting temperature or annealing point.

Table 1 sets forth the compositions of glasses, in parts by weight calculated from the batch, embodying the advantages of this invention together with the resistivities of each composition measured at 250 C. and 350 C. The measured resistivities .of each .example were compared to the resistivities of a corresponding glass wherein the Rb O was replaced by an equal molar amount of K 0 and the weight percent of SiO,, was adjusted to make the substitution possible, and the percentage increase in resistivity achieved by introducing the Rb O is shown.

Compositions of representative glasses in which- Rb o is absent are included for purposes of comparison.

Table I 68. 7 67. 0 60. 4 58. 7 57. 0 50. 4 4B. 7 10.0 10.0 20.0 20.0 20.0 30.0 30.0 0.1 0.1 0.1 0.1' 0.1 0.1 0.1 1.5 1. 5 1. 5 1. 5 1. 5 1. 5 1. 5 16.4 14. 8 18.0 16. 4 l4. 8 18.0 16.4 3.0 6.0 3.0 6.0 3.0 0.3 0.6 0.3 0.6 0.3 bzOan. 0.3 0.3 0. 3 0.3 0. 3 0. 3 0.3 Res. 250 0 10 (ohm.-

cm.) 2.9 3.8 3.8 6.2 8.6 6.6 10.8 Res-350 O. (10- (ohm.-

cm.) 4.7 4.7 6.1 8.5 10.7 9.3 12.2 Incr. Res. 250 0. (Percent) .81 138 63 126 64 Incr. Res. 350 0. (Percent) 42 42 39 31 47.0 38. 7 37.0 30.4 28. 7 27.0 30.0. 40.0 40.0 r 50.0 50.0 50.0 0.1 0.1 0.1 0.1 0.1 0.1 f 1.5 1.5 1.5 1.5 1.5 1.5 14. 8 16. 4 14. 8 18.0 16.4 14.8 6.0 3.0 6.0 3.0 6.0 0.6 0.3 0.6 .l 0.3 0.6 0.3 0.3 0.3 0.6 '0.3 0.3

(Percent) V 34 66 65 279 Incr. Res. 350 0.

(Percent) 44 18 24 16' 22 of 250 C. consisting essentially by weight of about 15% to 70% 'SiO 5% to 60% PbO, 5% to 25% alkali metal oxides, 0 to 5% A1 0 and a total of 0 to 15% alkaline earth metal oxides selected from the group consisting of MgO, CaO, and BaO, characterized in that R13 0 is pres- 5 cut in an amount that the ratio of Rb20 to total alkali metal oxide is about 1/20 to 3/10.

4. An alkali-lead-silicate glass of high electrical resistivity consisting essentially of about 39% SiO 51.5% PbO, 0.2% Na O, 5.1% K 0, 2.0% Rb O, 0.2% Cs o, 10 1.5% B210 and 0.5% As O References Cited in the file of this patent UNITED STATES PATENTS McAlpine et a1. Feb. 19, 1957 FOREIGN PATENTS 

3. A GLASS COMPOSITION HAVING AN ELECTRICAL RESISTIVITY GREATER THAN 1 MEGOHM WHEN MEASURED AT A TEMPERATURE OF 250*C. CONSISTING ESSENTIALLY BY WEIGHT OF ABOUT 15% TO 70% SIO2, 5% TO 60% PBO, 5% TO 25% ALKALI METAL OXIDES, 0 TO 5% AL2O3, AND A TOTAL OF 0 TO 15% ALKALINE EARTH METAL OXIDES SELECTED FROM THE GROUP CONSISTING OF MGO, CAO, AND BAO, CHARACTERIZED IN THAT RB2O IS PRESENT IN AN AMOUNT THAT THE RATIO OF RB20 TO TOTAL ALKALI METAL OXIDES IS ABOUT 1/20 TO 3/10. 